Add container readiness checks and exclude local state from images

Adapted from MikaelKW/nodecast-tv-plus readiness and container context work.

Co-authored-by: MikaelKW <87399352+MikaelKW@users.noreply.github.com>

scripts/healthcheck.cjs

@@ -0,0 +1,31 @@
+const http = require('node:http');
+
+function checkHealth(port = process.env.PORT || 3000, timeout = 4000) {
+    return new Promise(resolve => {
+        let settled = false;
+        const finish = healthy => {
+            if (settled) return;
+            settled = true;
+            clearTimeout(timer);
+            resolve(healthy);
+        };
+        const request = http.get({ host: '127.0.0.1', port, path: '/api/health' }, response => {
+            let body = '';
+            response.setEncoding('utf8');
+            response.on('data', chunk => {
+                body += chunk;
+                if (body.length > 4096) { finish(false); request.destroy(); }
+            });
+            response.on('error', () => finish(false));
+            response.on('end', () => {
+                try { finish(response.statusCode === 200 && JSON.parse(body).status === 'ok'); }
+                catch { finish(false); }
+            });
+        });
+        request.on('error', () => finish(false));
+        const timer = setTimeout(() => { finish(false); request.destroy(); }, timeout);
+    });
+}
+
+if (require.main === module) checkHealth().then(healthy => { process.exitCode = healthy ? 0 : 1; });
+module.exports = { checkHealth };